1. Field of the Invention
The present invention relates to a curve length measuring apparatus and particularly to a pen-holder type curve length measuring apparatus having a caster mechanism so as to be able to trace an object curved line correctly and easily.
2. Prior Art
There are curve length measuring apparatuses used for measuring the length of curves on maps, drawings and the like. Generally, these apparatuses are characterized in being used readily like drawing with a pencil. Therefore, most of the apparatuses have such a simple construction as comprising a pen-holder like body, a rolling disk provided at the tip of the body and an indicator mounted on the body. The rolling disk is for detecting a length of a curved or straight line by rolling the disk along the curve or the line. Since an axis of the rolling disk is rigidly connected with the body, while an operator traces curves with the rolling disk, the operator has to continue to rotate the body in the tangential direction of the curve, so it is difficult to trace curves correctly whose direction changes complicatedly. Further, it is hard to read the indicator due to the ever rotating body. These difficulties lead to incorrect or erroneous measurement of the curve length.